Studies of the innervation of rabbit myometrium and cervix

We characterized the innervation of isolated circular and longitudinal-oriented muscle strips from the nulliparous rabbit uterus and cervix by field stimulation (FS). FS with increasing frequency (2.5-50 pps) and voltage (2.5-70 V) caused graded increases in isometric contraction with no relaxation or inhibition of spontaneous activity. Tetrodotoxin (TTX, 3.1 x 10^-6 M) significantly reduced the FS response by 75% in all strips at higher stimulus frequencies. Contractile responses to FS were also significantly inhibited by atropine (3.5 x 10^-6 M) in circular uterus and in longitudinal cervix. Guanethidine (5 x 10^-6 M) reduced the response in all strips, as did phentolamine (3.6 x 10^-6) in longitudinal uterus and circular cervix. Propranolol (3.9 x 10^-6 M) did not significantly change the response in longitudinal uterus or circular cervix. In longitudinal uterus, combined guanethidine and atropine produced significant inhibition, but not statistically different from either drug alone. Similar results were seen in circular uterus. Electron microscopy and glyoxylic acid histofluorescences indicate that both blood vessels and smooth muscle in rabbit uterus are supplied with adrenergic nerves. The results suggest the presence of TTX-sensitive adrenergic and cholinergic excitatory innervation of rabbit uterus and cervix.